Carburetor



Jan. 15,1946. M E. CHANDLER CARBURETOR 7 Filed June 10, 1943 2Sheets-Sheet l N m o I m m 2 o H m zv I H w l A: 4 m 1 E F o (u N Q INVEN TOR. MILTON E. C HANDLER AGENT M. E. CHANDLER CARBURETOR Jan.15,1946.

2 Sheets-Sheet 2' Filed June 10, 1943 'Lbs. AIR How HY lie/3 INVENTOR.MIEI'ON E. CHANDLER AGENT Patented Jan. 15, 1946 CARBURETOR Milton E.Chandler, New Britain, Conn., assignor. to Chandler-Evans Corporation,South Merlden, Conn.,- a corporation of Delaware Application June 10,1943, Serial No. 490,281 g 4 Claims. (Cl. 261-39) This invention relatesto fluid flow measurement, and particularly to the measurement of theflow of a fluid subject to variations in density. This invention isparticularly useful in connection with the measurement of the quantityof air flowing through a carburetor in'an internal combustion engineadapted for use on aircraft.

In internal combustion engines; the most efficient conditions forcombustion are obtained when the mass of fuel supplied to the engine isproperly proportioned with respect to the mass .of air supplied. Inorder to obtain such combustion conditions, it has been proposed tomeasure the quantity of air flowing through the carburetor and tooperate a valve controlling the fuel flow in accordance with thequantity measured. It has been found that with such devices, themeasurement of the air is subject to error because of variations inthe'density in the air, so that the quantity of fuel is not properlyproportioned at all times.

It is, therefore, an object of this invention to provide improved meansfor measuring the flow of a fluid subject to variations in density.

Another object of the present invention is to provide an improvedcarburetor for use on aircraft, in which means is provided for measuringthe mass of the air flowing through the carburetor.

Another object of the present invention is to .provide improved fluidflow measuring means of the venturi meter type, in which means isprovided for correcting errors inherent in the Venturi meter.

A further object of the invention is to provide improved means formeasuring the flow off fluid through a conduit, including a Venturi tubein the conduit, a passage connecting the throat of the Venturi tube witha point in the conduit spaced from the venturi, means for restrictingthe flow of fluid through the passage so as to correct for inaccuraciesof the venturi, and means for-measuring a differential pressure in saidpassage.

Other objects and advantages of the present invention will becomeapparent from a consideration of the appended specification, claims, anddrawings, in which:

Figure 1 is a somewhat diagrammatic illustration of a carburetor for aninternal combustion engine embodying the principles of my invention,

Figure 2 is a. cross-sectional view of a. portion of a modified form ofcarburetor built in accord ance with my invention,

Figure 3 is a diagrammatic illustration of another modified form ofcarburetor utilizing the principles of my invention, and

Figure 4 is a, graphical illustration of the functional relationshipsbetween the air flow and the difierential pressures existing betweencertain points in a carburetor built in accordance with my invention.

Referring now to Figure 1, there is shown a carburetor body portion l0,having an air passage tached to the right end of the bellows.

valve 23 is so constructed that as the bellows extending therethroughfrom an inlet l2 to an outlet lit. The air passing through thecarburetor enters the inlet l2, and then flows past a venturi It, athrottle l5, and a fuel discharge nozzle l6.

A number of impact tubes I1 is located at the inlet l2. The open'ends ofthe tubes ll are exposed to the air entering the inlet l2. The tubes llare all connected to a passage l8, commonly termed a vent ring. Theimpact tubes H and thevent ring 3 form a part of a passage connect ingthe inlet I2 with the throat of the venturi It. This passage may betraced from the inlet l2 thru the impact tubes I1, vent ring 8, aconduit 20, a conduit 2I, a valve chamber 22, past a valve 23, througha, conduit 24, a restriction 25, a conduit 26, a chamber 21, and aconduit 28 to the throat of venturi It.

The valve 23 is operatedby a flexible bellows 30, which is mounted inthe chamber 21, and is therefore exposed, through the conduit 28, to thepressure existing at the throat of venturi It. The left end of thebellows 30, as it apears in the drawings, is fixed, and the valve 23 isat- The expands upon a drop in pressure in the chamber 21, the valve ismoved to open wider.

There is shown in Figure 4 a set of curves i1- lustrating therelationship between air flow through a Venturi tube such as that shownat It and the-square root of the pressure differential existing betweenthe throat of the tube and a point in the passage H spaced from thetube. The curves marked A and B in Figure 4 represent two curves madewith different pressures at the inlet l2. The curve A was made with alower value of inlet pressure, and hence lower density, than the curveB. The efiect of a variation in density on the relationship between airflow and difierential pressure may be observed by comparing curves A andB.

The straight line C in Figure 4 represents the relationship between airhow and the squareroot of the pressure difference which would be mostdesirable for purposes of measuring the air flow and controlling thefuel fiow from that measurement. 1. Since the ordinates in Figure 4 aremeasured;

C represents a pressure difference which varies as a parabolic functionof the air flowing through the carburetor. The curves at A and Billustrate pressure differentials which vary as exponential, butnon-parabolic, functions of the air flow. It should be observed that theordinates of the curves A and B, at any given air flow, are alwaysgreater than the ordinate of the straight line C.

In a Venturi type of measuring device, the pressure differentialobtained between the throat of the venturi and the end of the venturi isalways a non-parabolic function of the fluid flow. any particularordinate of which is greater than the corresponding ordinate of theparabolic function which would be ideal for measuring purposes. In otherwords, it may be stated that a venturi is subject to an inherent errorwhich causes the Venturi throat pressure to decrease more rapidly, orthe pressure diiference between entrance and throat to increase morerapidly, than the square of the velocity of the fluid flowing thru it. Ihave therefore provided means for obtaining a measuring pressuredifferential which is less than that existing between the throat and theend of the venturi, and which varies substantially as a parabolicfunction of thefluid flowing through the venturi.

In addition tothe error due to the inherent non-parabolic characteristicof a venturi, it may be seen by comparing the curves A and B of Figure4, that variations in the density of the fluid flowing through a Venturimeter cause the pressure differential between the throat and the end ofthe venturi to vary as a different nonparabolic function of the fluidflow for each different value of fluid density. I therefore provide inmyflow measuring device means for compensating the action of the Venturimeter for variations in the density in the flowing fluid.

In fact, I have provided an arrangement wherein Y a single valve isoperated so as to compensate the action of the Venturi meter both forthe inherent non-parabolic characteristic of the venturi, and forvariations in the density of the fluid flowing through the venturi.

This compensating means includes the valve 23 and the bellows 30 whichoperates the valve 23 in accordance with the variations in absolutepressure at the throat of the venturi it. Since the density of air isaifected not only by its pressure but also by its temperature, the

in terms of the square root of a pressure difference, it will beunderstood that the straight line increases.

bellows 30 is preferably filled with nitrogen, or

some other suitable fluid whose pressure varies with temperature, sothat the valve 23 is also operated in accordance with the temperature ofthe air flowing thru the passage II. It may be seen that the air flowingthrough the passage between the impact tube l1 and the throat of venturiI4 is subject to two restrictions in that passage, namely, the valve 23and the fixed may therefore be seen that the pressure differentialacross the valve 23 is less than the total pressure differential betweenthe end and throat of the venturi by an amount depending upon theconformation of the valve 23 and the temperature and pressure to whichthe bellows 30 is subjected.

Since the bellows 30 is subjected to the pressure at the throat of theventuri [4, it may be seen that as long as the density of the fluidpassing through the venturi is constant, the position of the valve 23varies as a non-parabolic function of the air flow through the venturiH. The eifect of this variation in the position of valve 23 is to reducethe pressure drop across the valve as the air flow through the venturiIt therefore opposes the effect of the pressure differential between thethroat and end of the venturi acting through the impact tubes H, whichis to increase the pressure differential across the valve 23 as the airflow through the venturi increases. I have found that by properlydesigning the conformation of valve 23 there may be obtained a pressuredifferential across the valve 23 which is substantially a true parabolicfunction of the air flow through the venturi l4;

Since the bellows 30 is filled with a fluid which varies in volume withthe pressure to which'the bellows is exposed, and since the bellows isexposed to a pressure of the fluid flowing through the venturi l4, itmay be seen that variations in density in the flowing fluid will causeexpansion and contraction in bellows 30 and operation of valve 23. Bycomparing curves A and B of Figure 4, it may be seen that a decrease indensity of the fluid flowing throughthe Venturi meter causes an increasein the pressure differential in the venturi out of proportion to thedesired parabolic relationship between the air flow and the pressuredifferential. This may be deduced from the fact that the curve A, in

which the error is greater, was made with fluid To summarize theforegoing, it may be stated that while the pressure difierential betweenthe end and throat of the venturi is an exponential. non-parabolicfunction of the air flow thru the venturi, the valve 23 isvoperated sothat the portion of the total pressure differential occurring across thevalve 23 is substantially a true parabolic function of the mas of airflowing thru the passage H.

In the carburetor illustrated in Figure 1, it is desired to proportionthe fuel flowing through the'carburetor l6 to the pressure drop existingacross the valve 23, so that optimum combustion conditions may beobtained in the engine on which the carburetor is mounted.

The fuel supply for they carburetor in 'gure 1 is obtained from a fuelpump or other source of fuel under pressure greater than atmospheric,and passes through a conduit 3|, a fuel regulaing valve unit generallyindicated at 32, a pair of metering restrictions 63 and 64, a conduit35,

a pressure regulating valve unit 36, and a conduit 31 to the dischargenozzle l6.

The flow regulating valve unit 32 comprises a balanced valve member 33,supported by a flexible diaphragm 34, which is attached 'at its edges tothe casing of the valve unit 32. The diaphragm 34 separates that casinginto a pair of expansible chambers 65 and 66, which are connected by aconduit 61 including a restriction 36. A spring 39 is located in thechamber 66, and biases the valve 33 for movement toward open position.

A portion of the fuel entering the chamber 65 is bled through therestriction 38 to chamber 66, and thence passes thru a conduit 46 to ametering unit generally indicated at 4|. The metering unit 4|' comprisesa casing 42 divided into four expansible chambers 43, 44, 45 and 46 bythree flexible diaphragms 41, 48 and 56. A sleeve carrying a valvemember 52 at one end thereof, is supported and positioned by the threediaphragms 41,48 and 56. The movements of sleeve 5| and the valve member52 are guided by a post anced valve member 51, which is attached to andpositioned by a flexible diaphragm 58, which is clamped at its edges inthe casing of the regulator unit 36. A compression spring 66 biases thevalve member 51 toward closed position. The diaphragm 58 divides thecasing of the regulator unit 36 into two chambers 56 and 6|. The chamber6| is connected, through a conduit 62, to the vent ring i6.

The function of the pressure regulator unit 36 is to maintain asubstantially constant pressure in the chamber 56 so that the flow offuel through the metering restrictions 63 and 64 is not affected bychanges in the pressure at the discharge nozzle |6 caused by variationsin the position of throttle l5. In the regulator unit 36, the pressurein the chamber 56 is balanced by the force of the spring 66. tweenchamber 6| and vent ring I8 is for purposes of venting the chamber only,so as to permit free movement of the diaphragm 58. The pressure inchamber 6| is so much smaller than the force of spring i8 and the forcedue to the pressure in chamber 56 that the pressure at the vent ring l6has substantially no controllin effect on the position of the diaphragm.

The quantity of fuel flowing through the carburetor is determined by theposition of valve 33 in the flow controlling unit 32. The position ofvalve 33 is in turn determined by the differential between the pressurein the chambers 65 and 66, and the force of the spring 36. Since thepressure on the downstream side of the jets 63 and 64 is maintainedsubstantially constant by the regulator unit 36, and the force of spring39 may also be considered as being constant, the pressure in the chamber65 may be taken as a measure of the quantity of fuel flowing through.the jets 63 and 64. In accordance with the laws of fluid flow, thepressur in chamber 65 is'a parabolic function of the fluid flow throughthe restrictions 63 and 64. The pressure in chamber Th connection be- 65is balanced against that in chamber 66, which is in turn controlled bythe metering unit 4|.

Chamber 45 of the metering unit 4| is connected through a conduit 16 andconduit 2| to the upstream side of valve 23. Chamber 44 of metering unit4| is connected through a conduit H to the downstream side of valve 23.Therefore the pressure differential between the chambers 44 and 45 is ameasure of the mass of air flowing through the passage 5|. This pressuredifferential acts on the sleeve 5| in a direction to close the valve 52against the seat 54. This closing tendency is resisted by the pressurein the chamber 43, which is the same as the pressure existing in chamber66 of fuel regulating unit 32 and therefore is a measure of the quantityof fuel entering the carburetor. The pressure in chamber 46 issubstantially constant, since it is connected to chamber 56, andtherefore normally has no regulating effect on the position of valve 52.The connection of chamber 46 through passage 55 to chamber 56 alsoprovides a convenient manner of disposing of the fuel passed through thevalve 52.

It may therefore be seen that in the carburetor of Figure 1, a pressurewhich varies as a parabolic function of the fuel flow is balancedagainst a pressure differential which varies as a parabolic function ofthe air flow, and that the fuel flow is regulated in accordance with thedifference between these two controlling forces.

Figure 2 There is shown in Figure 2 an arrangement by which theprinciples of my invention are applied to a rectangular carburetor ofthe type described and claimed in my co-pending application, Serial No.406,776, filed August 14, 1941, now U. S. Patent No. 2,361,993, issuedNovember 1'7, 1944'. In this arrangement there is shown a carburetorbody I66 through which extends an air passage |6| from an inlet NZ to anoutlet I63. The body I66 is of rectangular crosssection, andcarries fourparallel hollow Venturi members I64. A plurality of impact tubes I65have their open ends projected into the path of air entering into theinlet I62 trance to a passage extending from the inlet I62 to the throatof the venturi formed by the members I64. This passagev may :be tracedthrough the impact tubes I65, a vent ring I66, a conduit I61, arestriction I68, a conduit H6, past a valve into a valve chamber i2, andthence through a conduit M3 to the interior of the two Venturi membersH14 which are nearest the center of the passage Hit. It should be notedthat in this passage the fixed restriction and the variable restrictionformed by the valve are reversed in position with respect to thecorrespondin restrictions in the device of Figure 1. iable restrictionis nearest the throat of the venturi, whereas the fixed restriction wasnearest the Venturi throat in the construction of Figure 1. Furthermore,the pressure differential across the fixed restriction is connected tothe metering unit by the conduits l6 and H, which are connected to themetering unit in the same manner as the conduits l6 and ll of Figure 1.This is in contrast to the use of the pressure differential across thevariable restriction as the air metering pressure differential, which isillustrated in the device of Figure 1. It should be apparent, however,that the valve may be used to control the pressure difierential acrossthe fixed restricion in series with it, just as well as it can controlThe impact tubes |65 form the en- In other words, the var- 'air flowingthrough the passage IOI.

throat of the venturi.

the pressure differential across the valve itself.

The valve III is operated by a flexible bellows H4, whose rightend'isfixed to the carburetor body I00, and whose left end is attached to amovable plate H5 having a central projection which is adapted to engagethe left end of the valve III. A- compression spring IIG maintains thevalve III in engagement with the projection on the plate II5. A casingIII surrounds the bellows H4, form a closed chamber H8, which may befilled with nitrogen or other suitable material whose volume changes inaccordance with the variations of temperature and pressure adjacent thebellows H4. An extension I on the casing II 'I extends through anopening I 2i in the carburetor body I00 into the air passage II". Thetemperature v within the chamber I I8 is thereby made to follow moreclosely variations in the temperature in the Furthermore, the casing II!is located in a chamber in in the carburetor body I00 which is connectedthrough a conduit I23 through to interiors of-the Venturi members I04which lie adjacent the sides of the passage IOI, and are not used as apart of the metering passage between the end and Another conduit I24 connects a point in the chamber I22 remote from the conduit I23 with themain air passage IIlI at a point downstream from the throttles I25. Thepassage extending from the Venturi members I04 through the conduit I23and conduits I2I and I24 to the main air passage IOI insure a constantflow of air around the outside of the casing I I1 thereby providing fora more sensitive action of the bellows H4 in response to changes in thetemperature of the air flowing through the passage IOI.

Figure 3 There is shown in Figure 3 a modification of the carburetorillustrated in Figure l in which the fixed and variable restrictions inthe passage connecting the end and throat of the venturi are arranged inthe manner shown in Figure 2.

In Figure 3, the passage between the inlet and throat of the venturi maybe traced thru an impact tube I30, a vent ring I3I, a conduit I32, achamber I33 of a metering unit I34 which is substantially the same asthe metering unit M of Figure l, a conduit I35, a restriction I36, achamber I31 in the metering unit I34, a conduit I38, past a valve I40and through a chamber HI and a conduit I42 to the throat of the venturi.The valve I40 is operated by a flexible bellows I43.

It will be seen that in this arrangement, the pressure differentialmeasured by the metering unit I34 is that established across restrictionI36,

The casing and bellows together sure differential. In other words, thevalve must close in response to a decrease in pressure at the Venturithroat when the drop across the fixed restriction is used as themetering pressure differential( as in Figure 2), and the valve must openin response to a decrease in pressure at the Venturi throat when thedrop across the variable restriction is used as the metering pressuredifferential.

While I have shown and described certain preferred embodiments of myinvention, other modiflcations thereof will occur to those skilled inthe art and I therefore intend that my invention shall be limited onlyby the appended claims.

I claim as my invention:

1. A carburetor for an internal combustion engine, comprising incombination, a conduit of' thermostatic means for operating said valveto and this pressure difierential is controlled by the valve I40 in thesame manner as described in connection with Figure 1.

From a comparison of Figures 1 and 2, it should be apparent that theparticular sequence in which the flxed and variable restrictions arearranged in the passage connecting the end and throat of the venturi isof no particular importance as far as the operation of my improved fluidflow measuring means is concerned. Furthermore, it is possible toutilize either the pressure difierential across the fixed restriction orthe drop across the variable restriction as the flow metering pressuredifferential. Of course, the valve operation when the drop across thefixed restriction is used as the metering pressure differential must beopposite to the valve operation when the drop across the variablerestriction is used as the metering presvary the air flow thru saidpassage in accordance with the temperature of the air in said conduit,

a second passage connecting the interiors of certain others of saidmembers to a point in said conduit spacedfrom said Venturi means, saidthermostatic means being located in said second passage so as to beexposed to the air flowing therethru, and means responsive to thedifference in the pressures at spaced points in said first passage forcontrolling the flow of fuel thru said carburetor.

2. Apparatus for measurin the flow of a fluid of variable density,comprising a conduit for said fluid, a Venturi structure in saidconduit, a pair of independent passages connecting the throat of saidventuri to points in said conduit spaced from said throat, a pair ofrestrictions in series in one of said passages, a valve for varying thearea of one of said restrictions, means for operating said valveincluding a sealed expansible chamber having a fixed wall and aresiliently movable wall and filled with a fluid having an appreciablecoeflicient of thermal expansion, a second chamber located on theopposite side of said flxed wall from said movable wall and connected inthe other of said passages to be ventilated by the air flowingtherethru, said other passage being unrestricted so that the air flowingthru it is at substantially the same temperature as the air in saidconduit and is substantially unaifected by the temperature of thepassage walls, a third chamber located on the opposite side of saidmovable wall from said fixed wall and connected in said one passagebetween said restrictions and said throat, said chambers cooperating sothat the positions of said movable wall and valve are alfected by thetemperature in said-second chamber and the pressure in said thirdchamber, and means for measuring the pressure differential set up insaid one passage by one of said restrictions.

3. A carburetor for an internal combustion engine, comprising a bodyhaving a conduit extending therethru for combustion air flowing to saidengine, a venturi in said conduit, a pair of independent passagesconnecting the throat of said venturi to points in said conduit spacedfrom said throat, a pair of restrictions in serie in one of saidpassages, a valve for varying the area of one of said restrictions,means for operating said valve including a sealed expansible chamberhaving a fixed wall and a resiliently movable wall and filled with afluid having an appreciable coefficient of thermal expansion, a secondchamber located on the opposite side of said fixed Wall from saidmovable wall and connected in the other of said passages to beventilated by the air flowing therethru, said other passage beingunrestricted so that the air flowing thru it is at substantially thesame temperature as the air in said conduit and is substantiallyunaffected by the heat from said engine communicated thru the passagewalls, a third chamber located on the opposite side of said movable wallfrom said fixed wall and connected in said one passage between saidrestrictions and said throat, said chambers cooperating so that thepositions of said movable wall and valve are affected by the temperaturein said second chamber and the pressure in said third chamber, and meansresponsive to the pressure difierential set up in said one passage byone of said restrictions for controlling the flow of fuel to saidengine.

4. Apparatus for measuring the flow of a fluid of variable density,comprising a conduit for said fluid, a Venturi structure in saidconduit, a generally cylindrical chamber having aperipheral interiorshoulder, a cup-shaped casing mounted in said chamber with its rimengaging said shoulder so as to separate said chamber into two so ofsaid restrictions.

compartments, each said compartment having a pair of spaced portsopening therein, unrestricted passage means'connecting the respectiveports in the one of said compartments outside said casing to the throatof said venturi and to a point in said conduit spaced from said throatto ventilate said one compartment with air at substantially the sametemperature as the air in said main conduit, a flexible bellows mountedconcentrically within said casing and having one end fixed to the openend oi. said casing, a wall closing the free end of said bellows andforming with said bellows and casing an expansible chamber, a fluidhaving an appreciable coeificient of thermal expansion in saidexpansible chamber, a valve.

having a stem aligned with said wall, said valve cooperating with one ofthe ports in the other of said compartments, spring means biasing saidvalve stem into engagement with said wall so that it moves concurrentlytherewith, second passage means including a first section connecting theother port in said other compartment to,

the throat of said venturi and a second section connecting said one portin said other compartment to a point in said main conduit spaced fromsaid throat, said valve forming a restriction in said second section,another restriction in series in said second section, and means formeasuring the pressure difierential set up by one MILTON E. CHANDLER.

